The search for new therapeutic agents has been greatly aided in recent years by a better understanding of the structure of enzymes and other biomolecules associated with diseases. One important class of enzymes that has been the subject of extensive study is protein kinases.
Protein kinases constitute a large family of structurally related enzymes that are responsible for the control of a variety of signal transduction processes within the cell. (See, Hardie, G. and Hanks, S. The Protein Kinase Facts Book, I and II, Academic Press, San Diego, Calif.: 1995). Protein kinases are thought to have evolved from a common ancestral gene due to the conservation of their structure and catalytic function. Almost all kinases contain a similar 250–300 amino acid catalytic domain. The kinases may be categorized into families by the substrates they phosphorylate (e.g., protein-tyrosine, protein-serine/threonine, lipids, etc.). Sequence motifs have been identified that generally correspond to each of these kinase families (See, for example, Hanks, S. K., Hunter, T., FASEB J. 1995, 9, 576–596; Knighton et al., Science 1991, 253, 407–414; Hiles et al., Cell 1992, 70, 419–429; Kunz et al., Cell 1993, 73, 585–596; Garcia-Bustos et al., EMBO J. 1994, 13, 2352–2361).
In general, protein kinases mediate intracellular signaling by effecting a phosphoryl transfer from a nucleoside triphosphate to a protein acceptor that is involved in a signaling pathway. These phosphorylation events act as molecular on/off switches that can modulate or regulate the target protein biological function. These phosphorylation events are ultimately triggered in response to a variety of extracellular and other stimuli. Examples of such stimuli include environmental and chemical stress signals (e.g., osmotic shock, heat shock, ultraviolet radiation, bacterial endotoxin, and H2O2), cytokines (e.g., interleukin-1 (IL-1) and tumor necrosis factor α (TNF-α)), and growth factors (e.g., granulocyte macrophage-colony-stimulating factor (GM-CSF), and fibroblast growth factor (FGF)). An extracellular stimulus may affect one or more cellular responses related to cell growth, migration, differentiation, secretion of hormones, activation of transcription factors, muscle contraction, glucose metabolism, control of protein synthesis, and regulation of the cell cycle.
Many diseases are associated with abnormal cellular responses triggered by protein kinase-mediated events as described above. These diseases include, but are not limited to, autoimmune diseases, inflammatory diseases, bone diseases, metabolic diseases, neurological and neurodegenerative diseases, cancer, cardiovascular diseases, allergies and asthma, Alzheimer's disease, and hormone-related diseases. Accordingly, there has been a substantial effort in medicinal chemistry to find protein kinase inhibitors that are effective as therapeutic agents.
Glycogen synthase kinase-3 (GSK-3) is a serine/threonine protein kinase comprised of α and β isoforms that are each encoded by distinct genes [Coghlan et al., Chemistry & Biology 2000, 7, 793–803; and Kim and Kimmel, Curr. Opinion Genetics Dev., 2000 10, 508–514]. GSK-3 has been implicated in various diseases including diabetes, Alzheimer's disease, CNS disorders such as manic depressive disorder and neurodegenerative diseases, and cardiomyocyte hypertrophy [PCT Application Nos.: WO 99/65897 and WO 00/38675; and Haq et al., J. Cell Biol. 2000, 151, 117–130]. These diseases are associated with the abnormal operation of certain cell signaling pathways in which GSK-3 plays a role. GSK-3 has been found to phosphorylate and modulate the activity of a number of regulatory proteins. These proteins include glycogen synthase, which is the rate limiting enzyme necessary for glycogen synthesis, the microtubule associated protein Tau, the gene transcription factor β-catenin, the translation initiation factor e1F2B, as well as ATP citrate lyase, axin, heat shock factor-1, c-Jun, c-myc, c-myb, CREB, and CEPBα. These diverse protein targets implicate GSK-3 in many aspects of cellular metabolism, proliferation, differentiation, and development.
In a GSK-3 mediated pathway that is relevant for the treatment of type II diabetes, insulin-induced signaling leads to cellular glucose uptake and glycogen synthesis. Along this pathway, GSK-3 is a negative regulator of the insulin-induced signal. Normally, the presence of insulin causes inhibition of GSK-3 mediated phosphorylation and deactivation of glycogen synthase. The inhibition of GSK-3 leads to increased glycogen synthesis and glucose uptake [Klein et al., PNAS 1996, 93, 8455–8459; Cross et al., Biochem. J. 1994, 303, 21–26); Cohen, Biochem. Soc. Trans. 1993, 21, 555–567; and Massillon et al., Biochem J. 1994, 299, 123–128]. However, in a diabetic patient, where the insulin response is impaired, glycogen synthesis and glucose uptake fail to increase despite the presence of relatively high blood levels of insulin. This leads to abnormally high blood levels of glucose with acute and long-term effects that may ultimately result in cardiovascular disease, renal failure and blindness. In such patients, the normal insulin-induced inhibition of GSK-3 fails to occur. It has also been reported that in patients with type II diabetes, GSK-3 is overexpressed [see, PCT Application: WO 00/38675]. Therapeutic inhibitors of GSK-3 are therefore potentially useful for treating diabetic patients suffering from an impaired response to insulin.
GSK-3 activity is also associated with Alzheimer's disease. This disease is characterized by the well-known β-amyloid peptide and the formation of intracellular neurofibrillary tangles. Aβ peptides are derived from the amyloid precursor protein (APP) by sequential proteolysis, catalysed by the aspartyl protease BACE2, followed by presenilin-dependent γ-secretase cleavage. It has been demonstrated that antibodies against β-amyloid plaques can slow cognitive decline in patients with Alzheimer's disease (Hock et al., Neuron, 2003, 38, 547–554), and thus other β-amyloid-lowering strategies (e.g., the development of agents capable of inhibiting β-amyloid peptide) would be useful in the treatment of Alzherimer's disease and other psychotic and neurodegenerative disorders. Additionally, the neurofibrillary tangles contain hyperphosphorylated Tau protein, in which Tau is phosphorylated on abnormal sites, and thus agents capble of inhibiting the hyperphosphorylation of Tau protein would be useful in the treatment of Alzherimer's disease and other psychotic and neurodegenerative disorders.
GSK-3 is known to phosphorylate these abnormal sites in cell and animal models. Furthermore, inhibition of GSK-3 has been shown to prevent hyperphosphorylation of Tau in cells [Lovestone et al., Current Biology 1994, 4, 1077–86; and Brownlees et al., Neuroreport 1997, 8, 3251–55]. Therefore, GSK-3 activity promotes generation of the neurofibrillary tangles and the progression of Alzheimer's disease. It has also been shown that GSK-3 facilitates APP processing and that a GSK-3 inhibitor (lithium) inhibits of the generation of Aβ peptides through the inhibition of GSK-3 (Phiel et al. Nature 2003, 423, 435–439). Thus, the development of inhibitors of GSK-3 would be useful for the reduction of the formation of amyloid plaques and neurofibrillry tangles, the pathological hallmarks of Alzheimer's Disease, and would also be useful for the treament of other psychotic and neurodegenerative disorders.
Another substrate of GSK-3 is β-catenin, which is degradated after phosphorylation by GSK-3. Reduced levels of β-catenin have been reported in schizophrenic patients and have also been associated with other diseases related to increase in neuronal cell death [Zhong et al., Nature 1998, 395, 698–702; Takashima et al., PNAS 1993, 90, 7789–93; and Pei et al., J. Neuropathol. Exp 1997, 56, 70–78].
GSK-3 activity is also associated with stroke [Wang et al., Brain Res 2000, 859, 381–5; Sasaki et al., Neurol Res 2001, 23, 588–92; Hashimoto et al., J. Biol. Chem 2002, 277, 32985–32991].
The Janus kinases (JAK) are a family of tyrosine kinases consisting of JAK1, JAK2, JAK3 and TYK2. The JAKs play a critical role in cytokine signaling. The down-stream substrates of the JAK family of kinases include the signal transducer and activator of transcription (STAT) proteins. JAK/STAT signaling has been implicated in the mediation of many abnormal immune responses such as allergies, asthma, autoimmune diseases such as transplant rejection, rheumatoid arthritis, amyotrophic lateral sclerosis and multiple sclerosis as well as in solid and hematologic malignancies such as leukemias and lymphomas. The pharmaceutical intervention in the JAK/STAT pathway has been reviewed [Frank Mol. Med. 5: 432–456 (1999) & Seidel, et al, Oncogene 19: 2645–2656 (2000)].
JAK1, JAK2, and TYK2 are ubiquitously expressed, while JAK3 is predominantly expressed in hematopoietic cells. JAK3 binds exclusively to the common cytokine receptor gamma chain (γc) and is activated by IL-2, IL-4, IL-7, IL-9, and IL-15. The proliferation and survival of murine mast cells induced by IL-4 and IL-9 have, in fact, been shown to be dependent on JAK3- and γc-signaling [Suzuki et al, Blood 96: 2172–2180 (2000)].
Cross-linking of the high-affinity immunoglobulin (Ig) E receptors of sensitized mast cells leads to a release of proinflammatory mediators, including a number of vasoactive cytokines resulting in acute allergic, or immediate (type I) hypersensitivity reactions [Gordon et al, Nature 346: 274–276 (1990) & Galli, N. Engl. J. Med., 328: 257–265 (1993)]. A crucial role for JAK3 in IgE receptor-mediated mast cell responses in vitro and in vivo has been established [Malaviya, et al, Biochem. Biophys. Res. Commun. 257: 807–813 (1999)]. In addition, the prevention of type I hypersensitivity reactions, including anaphylaxis, mediated by mast cell-activation through inhibition of JAK3 has also been reported [Malaviya et al, J. Biol. Chem. 274:27028–27038 (1999)]. Targeting mast cells with JAK3 inhibitors modulated mast cell degranulation in vitro and prevented IgE receptor/antigen-mediated anaphylactic reactions in vivo.
A recent study described the successful targeting of JAK3 for immunosuppression and allograft acceptance. The study demonstrated a dose-dependent survival of Buffalo heart allograft in Wistar Furth recipients upon administration of inhibitors of JAK3 indicating the possibility of regulating unwanted immune responses in graft versus host disease [Kirken, transpl. proc. 33: 3268–3270 (2001)].
IL-4-mediated STAT-phosphorylation has been implicated as the mechanism involved in early and late stages of rheumatoid arthritis (RA). Up-regulation of proinflammatory cytokines in RA synovium and synovial fluid is a characteristic of the disease. It has been demostrated that IL-4-mediated activation of IL-4/STAT pathway is mediated through the Janus Kinases (JAK 1 & 3) and that IL-4-associated JAK kinases are expressed in the RA synovium [Muller-Ladner, et al, J. Immunol. 164: 3894–3901 (2000)].
Familial amyotrophic lateral sclerosis (FALS) is a fatal neurodegenerative disorder affecting about 10% of ALS patients. The survival rates of FALS mice were increased upon treatment with a JAK3 specific inhibitor. This suggested that JAK3 plays a role in FALS [Trieu, et al, Biochem. Biophys. Res. Commun. 267: 22–25 (2000)].
Signal transducer and activator of transcription (STAT) proteins are activated by, among others, the JAK family kinases. Results from a recent study suggested the possibility of intervention in the JAK/STAT signaling pathway by targeting JAK family kinases with specific inhibitors for the treatment of leukemia [Sudbeck, et al, Clin. Cancer Res. 5: 1569–1582 (1999)]. JAK3 specific compounds were shown to inhibit the clonogenic growth of JAK3-expressing cell lines DAUDI, RAMOS, LC1; 19, NALM-6, MOLT-3 and HL-60.
In animal models, TEL/JAK2 fusion proteins have induced myeloproliferative disorders and in hematopoietic cell lines, introduction of TEL/JAK2 resulted in activation of STAT1, STAT3, STAT5, and cytokine-independent growth [Schwaller, et al, EMBO J. 17: 5321–5333 (1998)].
Inhibition of JAK3 and TYK2 abrogated tyrosine phosphorylation of STAT3, and inhibited cell growth of mycosis fungoides, a form of cutaneous T cell lymphoma. These results implicated JAK family kinases in the constitutively activated JAK/STAT pathway that is present in mycosis fungoides [Nielsen, et al, Proc. Nat. Acad. Sci. U.S.A. 94: 6764–6769 (1997)]. Similarly, STAT3, STAT5, JAK1 and JAK2 were demonstrated to be constitutively activated in mouse T cell lymphoma characterized initially by LCK over-expression, thus further implicating the JAK/STAT pathway in abnormal cell growth [Yu, et al, J. Immunol. 159: 5206–5210 (1997)]. In addition, IL-6-mediated STAT3 activation was blocked by an inhibitor of JAK, leading to sensitization of myeloma cells to apoptosis [Catlett-Falcone, et al, Immunity 10:105–115 (1999)].
PIM-1 is the protooncogene activated by murine leukemia virus (Provirus Integration site for Moloney murine leukemia virus) [Cuypers, H. T., et al., Cell 37, 141–150 (1984)]. The expression of the protoconcogene produces a non-transmembrane serine/threonine kinase of 313 residues, including a kinase domain consisting of 253 amino acid residues. Two isoforms are known through alternative initiation (p44 and p33) [Saris, C. J. M., et al., EMBO J., 10, 655–664 (1991)]. Two PIM-1 homologs have been described [Baytel, D., Biochim Biophys Acta 1442, 274–85 (1998); Feldman, J., et al., J Biol Chem 273, 16535–16543(1998)]. PIM-2 and PIM-3 are respectively 58% and 69% identical to Pim-1 at the amino acid level. PIM-1 is highly expressed in the liver and spleen during hematopoiesis, and expression is induced by cytokines such as GM-CSF, G-SCF, IL-3, IF-α, and IL-6 [Lilly, M., et al., Oncogene 7, 727–732 (1992); Sato, N., et al., EMBO J. 12, 4181–4189 (1993); Jaster, R.,et al., Cell Signal 11, 331–335 (1999); Matikainen, S., et al., Blood 93, 1980–1991 (1999)].
PIM-1 has been implicated in lymphoma development. Induced expression of PIM-1 and the protooncogene c-myc synergize to increase the incidence of lymphomagenesis [Breuer M., et al., Nature 340, 61–63 (1989); van Lohuizen M., et al., Cell 65, 737–52 (1991)]. PIM-1 functions in cytokine signaling pathways and has been shown to play a role in T cell development [Schmidt, T., et al., EMBO J 17, 5349–5359 (1998); Jacobs, H., et al., JEM 190, 1059–1068 (1999)]. Signaling through gp130, a subunit common to receptors of the IL-6 cytokine family, activates the transcription factor STAT3 and can lead to the proliferation of hematopoietic cells [Hirano, T., et al., Oncogene 19, 2548–2556 (2000)]. A kinase-active PIM-1 appears to be essential for the gp130-mediated STAT3 proliferation signal. In cooperation with the c-myc PIM-1 can promote STAT3-mediated cell cycle progression and antiapoptosis [Shirogane, T., et al., Immunity 11, 709–719 (1999)]. PIM-1 also appears to be necessary for IL-3-stimulated growth in bone marrow-derived mast cells [Domen J., et al., Blood 82, 1445–52 (1993)] and survival of FDCP1 cells after IL-3 withdrawal [Lilly, M., et al., Oncogene 18, 4022–4031 (1999)].
Additionally, control of cell proliferation and survival by PIM-1 may be effected by means of its phosphorylation of the well established cell cycle regulators cdc25 [Mochizuki , T., et al., J Biol Chem 274, 18659–18666 (1999)] and/or p21(Cip1/WAF1)[ Wang, Z., et al., Biochim Biophys Acta 1593, 45–55 (2002)] or phosphorylation of heterochromatin protein 1, a molecule involved in chromatin structure and transcriptional regulation [Koike N., et al., FEBS Lett 467, 17–21 (2000)].
Both FLT-3 and c-Kit belong to a family of receptor tyrosine kinases, including PDGF-receptor and c-Fms [Scheijen, B, Griffin J D, Oncogene, 21, 3314–3333 (2002)]. FLT-3 and c-Kit regulate maintenance of stem cell/early progenitor pools as well the development of mature lymphoid and myeloid cells [Lyman, S, Jacobsen, S, Blood, 91, 1101–1134 (1998)]. Both receptors contain an intrinsic kinase domain that is activated upon ligand mediated dimerization of the receptors. Upon activation, the kinase domain induces autophosphorylation of the receptor as well as the phosphorylation of various cytoplasmic proteins that help propogate the activation signal leading to growth, differentiation and survival. Some of the downstream regulators of FLT-3 and c-Kit receptor signaling include, PLCγ, PI3-kinase, Grb-2, SHIP and Src related kinases [Scheijen, B, Griffin J D, Oncogene, 21, 3314–3333 (2002)]. Both receptor tyrosine kinases have been shown to play a role in a variety of hematopoietic and non-hematopoietic malignancies. Mutations that induce ligand independent activation of FLT-3 and c-Kit have been implicated acute-myelogenous leukemia (AML), acute lymphocytic leukemia (ALL), mastocytosis and gastrointestinal stromal tumor (GIST). These mutations include single amino acid changes in the kinase domain or internal tandem duplications, point mutations or in-frame deletions of the juxtamembrane region of the receptors. In addition to activating mutations, ligand dependent (autocrine or paracrine) stimulation of over-expressed wild-type FLT-33 or c-Kit can contribute to the malignant phenotype [Scheijen, B, Griffin J D, Oncogene, 21, 3314–3333 (2002)].
The 3-phosphoinositide-dependent protein kinase-I (PDK1) plays a key role in regulating the activity of a number of kinases belonging to the AGC subfamily of protein kinases (Alessi, D. et al., Biochem. Soc. Trans, 2001, 29, 1). These include isoforms of protein kinase B (PKB, also known as Akt), p70 ribosomal S6 kinase (S6K) (Avruch, J. et al., prog. Mol. Subcell. Biol., 2001, 26, 115), and p90 ribosomal S6 kinase (Frodin, M. et al., EMBO, 2000, 19, 2924). PDK1 mediated signaling is activated in response to insulin and growth factors and as a consequence of attachment of the cell to the extracellular matrix (integrin signaling). Once activated these enzymes mediate many diverse cellular events by phosphorylating key regulatory proteins that play important roles controlling processes such as cell survival, growth, proliferation and glucose regulation (Lawlor, M. A. et al., J. Cell Sci., 2001, 114, 2903: Lawlor, M. A. et al., EMBO J., 2002 21, 3728). PDK1 is a 556 amino acid protein, with an N-terminal catalytic domain and a C-terminal pleckstrin homology (PH) domain, which activates its substrates by phosphorylating these kinases at their activation loop (Belham, C. et al., Curr. Biol., 1999 9, R93). Many human cancers including prostate and NSCL have elevated PDK1 signaling pathway function resulting from a number of distinct genetic events such as PTEN mutations or over-expression of certain key regulatory proteins (Graff, J. R., Expert Opin. Ther. Targets, 2002, 6, 103: Brognard, J., et al., Cancer Res., 2001, 61, 3986). Inhibition of PDK1 as a potential mechanism to treat cancer was demonstrated by transfection of a PTEN negative human cancer cell line (U87MG) with antisense oligonucleotides directed against PDK1. The resulting decrease in PDK1 protein levels led to a reduction in cellular proliferation and survival (Flynn, P., et al., Curr. Biol., 2000, 10, 1439). Consequently the design of ATP binding site inhibitors of PDK1 offers, amongst other treatments, an attractive target for cancer chemotherapy.
Syk is a tyrosine kinase that plays a critical role in FcεRI mediated mast cell degranulation and eosiniphil activation. Accordingly, Syk kinase is implicated in various allergic disorders, in particular asthma. It has been shown that Syk binds to the phosphorylated gamma chain of the FcεRI receptor via N-terminal SH2 domains and is essential for downstream signaling [Taylor et al, Mol Cell Biol 1995; 15:4149].
Inhibition of eosinophil apoptosis has been proposed as key mechanisms for the development of blood and tissue eosinophilia in asthma. IL-5 and GM-CSF are upregulated in asthma and are proposed to cause blood and tissue eosinophilia by inhibition of eosinophil apoptosis. Inhibition of eosinophil apoptosis has been proposed as a key mechanism for the development of blood and tissue eosinophilia in asthma. It has been reported that Syk kinase is required for the prevention of eosinophil apoptosis by cytokines (using antisense) [Yousefi et al, J Exp Med 1996;183:1407].
The role of Syk in FcγR dependent and independent response in bone marrow derived macrophages has been determined by using irradiated mouse chimeras reconstituted with fetal liver cells from Syk −/− embryos. Syk deficient macrophages were defective in phagocytosis induced by FcγR but showed normal phagocytosis in response to complement [Kiefer et al, Mol Cell Biol 1998; 18:4209]. It has also been reported that aerosolized Syk antisense suppresses Syk expression and mediator release from macrophages [Stenton et al, J Immunology 2000; 164: 3790].
There is a continued need to find new therapeutic agents to treat human diseases. Accordingly, there is a great need to develop inhibitors of GSK-3, JAK, FLT-3, PIM-1, SYK, and PDK-1 protein kinases that are useful in treating various diseases or conditions associated with GSK-3, JAK, FLT-3, PIM-1, SYK, and PDK-1 activation, particularly given the inadequate treatments currently available for the majority of these disorders.